I used the one in my gym for the first time properly and it seemed pretty good. Gets me out of the habit of just punching straight forward as i was doing on the heavy bag and actually aiming for something. Also the height adjustablility is pretty cool and the legs seem good for training low kicks.

It was only filled with water and so wasn't as sturdy as it could have been but the fact that it moves when you hit it means you're not just standing in the one spot whilst working out, so you get some sort of 'swing' if you like.

I think it's a good way to supplement heavy bag training, but not replace it completely so i will still be using heavy bags at the gym.

Any opinions from people that have used them for a prolonged period of time?

A man who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself. - John Stuart Mill